Evidence for the N′(1720)3/2+ nucleon resonance from combined studies of CLAS π+π−p photo- and electroproduction data

Abstract

The analysis of the nine 1-fold differential cross sections for the γr,vp→π+π−p photo- and electroproduction reactions obtained with the CLAS detector at Jefferson Laboratory was carried out with the goal to establish the contributing resonances in the mass range from 1.6 GeV to 1.8 GeV. In order to describe the photo- and electroproduction data with Q2-independent resonance masses and hadronic decay widths in the Q2 range below 1.5 GeV2, it was found that an N′(1720)3/2+ state is required in addition to the already well-established nucleon resonances. This work demonstrates that the combined studies of π+π−p photo- and electroproduction data are vital for the observation of this resonance. The contributions from the N′(1720)3/2+ state and the already established N(1720)3/2+ state with a mass of 1.745 GeV are well separated by their different hadronic decays to the πΔ and ρp final states and the different Q2-evolution of their photo-/electroexcitation amplitudes. The N′(1720)3/2+ state is the first recently established baryon resonance for which the results on the Q2-evolution of the photo-/electrocouplings have become available. These results are important for the exploration of the nature of the “missing” baryon resonances.

Keywords

• Two pion production
• Resonance couplings
• Missing resonances